Heat inactivation of enteric viruses in dewatered wastewater sludge

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Abstract
The effect of moisture content on the rates of heat inactivation of enteric viruses in wastewater sludge was determined. The protective effect of raw sludge on poliovirus previously observed (R. L. Ward, C. S. Ashley, and R. H. Moseley, Appl. Environ. Microbiol. 32:339--346, 1976) was found to be greatly enhanced in sludge dewatered by evaporation. Other enteroviruses responded in a similar fashion. This effect did not appear to be due merely to the state of dryness of the sludge samples because in humus-deficient soil, a relatively inert material, the rate of poliovirus inactivation by heat was not significantly altered through dewatering. Instead, this effect appeared to have been caused by protective substances in the sludge, such as detergents, which are concentrated through dewatering. As reported previously (R. L. Ward and C. S. Ashley, Appl. Environ. Microbiol. 34:681-688, 1977; R. L. Ward and C. S. Ashley, Appl. Environ. Microbiol 36:889--897, 1978) raw sludge is not protective of reovirus, but, instead, the ionic detergents in sludge cause the rate of heat inactivation of this virus to be accelerated. Dewatering of sludge, however, was found to partially reverse this virucidal effect. Evidence is presented indicating that this reversal is caused by an unidentified protective substance in sludge also concentrated through dewatering. Finally, it was shown that the effects of raw sludge on heat inactivation of poliovirus and reovirus are greatly reduced by composting, a result that correlated with the degradation of detergents.